Apparatus and methods are known to identify, in situ, tumorous masses in biological tissue by using the electrical properties of such tissue, for example, by determination of electrical impedance or dielectric constants. It is also known that some benign and malignant tumors may be determined from differences in the measured electrical properties of such tissue.
It has been reported, for example, in T. Morimoto, et al., "Measurement of the Electrical Bio-Impedance of Breast Tumors," European Surgical Research, Vol. 22, pg. 86-92 (1990), that there are measurable differences between the electrical impedances of normal breast tissue, benign breast tumors, and malignant breast tumors. That paper describes a coaxial electrode arrangement wherein current pulses are conducted from an outer conductor of the electrode to a ground plate while voltage between an inner conductor of the electrode and the ground plate is sensed to determine tissue impedance.
Apparatus and methods are also known for causing in situ necrosis of tumorous masses, such as by hyperthermia (raising the temperature of biological tissue through inductive, radiant, contact, and joulean heating methods), the use of ionizing radiation (e.g., X-ray therapy), and cryosurgery. Several such devices are described in U.S. Pat. Nos. 4,016,886 and 4,121,592 (hyperthermia); U.S. Pat. No. Re 34,421 (ionizing radiation); and U.S. Pat. No. 4,140,109 (cryosurgery).
It is further known, for example by McRae U.S. Pat. No. 5,069,223, that the electrical impedance of an identified tissue mass may be measured to determine the progress resulting from hyperthermic treatment. McRae describes an electrode-bearing probe that may be inserted into biological tissue to sense the change in electrical impedance induced by a separate heating applicator.
A drawback of the above-described previously known apparatus and methods is that a first device is used for characterizing the biological tissue (e.g., whether tissue is malignant or nonmalignant) and a second, separate, device is then required for treating the tissue. For example, the device described in the Morimoto reference may be used to identify a tumorous tissue mass. The identified tissue mass may then be treated, for example, by hyperthermia, by positioning a treatment device at the proper location and actuating it. Finally, a method such as described in the McRae patent may be used to sense the electrical impedance of the tissue exposed to hyperthermia to monitor the progress of the therapeutic treatment.
Since the step of characterizing a target tissue is performed independently of the step of positioning the treatment device, within or adjacent to that tissue, previously known apparatus and methods do not provide accurate registration between the measuring device and the treatment device. Consequently, the potential arises for incompletely treating the intended tissue mass, thus leaving intact tumorous cells, or alternatively causing extensive necrosis to healthy tissue to avoid incomplete treatment. Moreover, these previously known techniques and devices are excessively invasive and the sequential or combined nature of their use may result in significant patient discomfort.
In view of the foregoing, it would be desirable to provide apparatus and methods in which a single instrument is used both to characterize and to treat tumors in situ. The ability to characterize and treat tumors with a single instrument would significantly reduce the invasiveness required in the characterization and treatment of tumors in accordance with previously known apparatus and methods.
It would also be desirable to provide apparatus and methods for conducting in situ characterization and treatment of tissue, using a single device, to improve the efficiency of the medical procedure and to reduce patient distress during the medical procedure.
It would also be desirable to provide apparatus and methods for in situ characterization and treatment of tissue that provides a high degree of registration between the measuring apparatus and the treatment apparatus, thereby providing the ability to treat tissue adequately without excessive damage to neighboring healthy tissue.